1. Field of the Invention
The invention relates to a vibration control device for a sewing machine designed to actively reduce vibration generated in a machine body by the rotation of an arm shaft, vertical reciprocation of a needle bar, and similar movements.
2. Description of the Related Art
Conventionally, various techniques of suppressing the generation of vibration in a sewing machine have been provided. Some typical techniques will be described with reference to FIG. 11, showing the internal structure of a machine body of a sewing machine in the prior art.
In a first technique, the total mass of a needle bar 940 and a needle bar connecting stud 946, that vertically reciprocates together with the needle bar 940, is reduced to thereby reduce the vibration generated by the vertical reciprocation of the needle bar 940. For example, the material of the needle bar 940 is changed from a steel material in the form of solid round bar to an aluminum material in the form of hollow bar, thereby reducing the mass of the needle bar 940.
In a second technique, the vibration generated by the vertical reciprocation of the needle bar 940, the vibration generated by the swing motion of a thread take-up lever 936, and the vibration generated by the motion of other parts associated with the needle bar 940 and the thread take-up lever 936 are intended to be canceled by the vibration generated by the rotation of a thread take-up crank 934 associated with the needle bar 940 and the thread take-up lever 936. The material, size, and location of each part are determined so as to reduce the vibration.
In a third technique, the wall thickness of an arm 922 is increased to increase the rigidity of the arm 922, thereby suppressing the generation of vibration.
In a fourth technique, there is provided a simple device for generating a waveform with a phase that is reversed to that of the vibration generated by vertical reciprocation of the needle bar 940 to suppress the vibration of the sewing machine.
However, in the first technique, the mechanical strength of the mechanism as a whole is reduced. Therefore, to limit the reduction in mechanical strength, the reduction of the mass is limited and the reduction in vibration is accordingly limited.
In the second technique, the needle bar 940, the thread take-up lever 936, and the other parts, including the thread take-up crank 934 moving in association with the parts 940,936, produce complex mutual motions which are high-speed motions. Therefore, it is very difficult to design all the parts sufficiently in balance so as to reduce the vibration.
In the third technique, a cost of parts is increased. Further, the increase in rigidity of the arm 922 causes an increase in the total weight of the sewing machine, departing from an intention of the design to reduce the weight of the sewing machine and thereby facilitate handling by an operator.
Finally in the fourth technique, it is very difficult to precisely attain a waveform with the same amplitude and the reverse phase to the vibration caused by the high-speed rotation of the arm shaft 931 of the sewing machine. Further, in actuality, the vibration of the sewing machine suffers from an influence of the disturbance, and the time delay in the vibration transfer system, as well as other equally complex considerations. Therefore, it is considered impossible to accurately track and suppress the vibration.